The present invention relates to swimming flippers, and in particular to flippers substantially consisting of a blade and a shaped shoe, said shaped shoe being made of an elastomeric material, rubber for instance, and said blade being made of a harder material, for instance of thermosetting resin with high values of hardness and mechanical resistance.
It is known that while swimming the scuba diver substantially makes with each flipper, synchronously and continuously, two kinds of movement or flipping: a movement down-up with respect to the water surface, i.e. the active flipping, which begins with the flipper having a strong inclination with respect to said surface, and a movement up-down, i.e. the passive flipping, which begins with the flipper being almost parallel to the water surface. Moreover, in the active flipping going upwards the lower surface of the flipper blade acts onto the water mass in touch with it and thus ensures a good forward thrust for the scuba diver, whereas in the passive flipping going downwards it is the upper surface or back of the blade which acts on the water mass in touch with it and substantially under it, said blade being located, as was said before, in an almost parallel position to the water surface, so that the forward thrust at this stage is rather limited.
From U.S. Pat. No. 3,171,142 a swimming flipper is known comprising a shoe provided with a sole to which a flexible blade is secured, and further comprising two pairs of abutment rods secured to said sole and disposed longitudinally each on one side of said blade for limiting the amplitude of the stroke of the blade. The described device is very difficult to be mounted on a swimming flipper.
From U.S. Pat. No. 2,343,468 a propulsion device for swimmers is known, which is very similar to the device of U.S. Pat. No. 3,171,142 previously mentioned. This device is even more unpractical than the device described in U.S. Pat. No. 3,171,142.
From U.S. Pat. No. 3,256,540 a swimming flipper is known comprising a shoe element and a blade element. According to said prior art patent, the shoe element is hinged at the heel region to the blade element, and flexible tie means are provided between shoe and blade for limiting the angular stroke of the blade with respect to the shoe. Again, this device is very difficult to be realized.